Everybody knows about the small lizard that can change its color whenever it wants and most of us have wondered how this is possible. Now scientists have the answer to this. A study was conducted on panther chameleons, namely five adult males, four adult females and four juveniles. Panther chameleons can be found in Madagascar and are quite popular as pets The research was done at the University of Geneva with Prof Michel Milinkovitch as the main author and evolutionary biologists together with quantum physicists as part of the team. The study was published in the Nature Communication journal.
It was already suspected that the chameleon’s ability to change its color comes from collecting or dispersing pigments of color inside distinct cells. The new study suggests that the selection of the colored pigments is made by crystals, which form “a selective mirror”. In addition, it seems that chameleons have a second layer of cells that helps the reptile keep cold by reflecting the near-infrared light.
The color of their skin can be changed either through mixing or by shifting pigments. Chameleons have cells with pigments for both dark and warm colors. But because of the fact that the light rebounds off physical elements such as the previously mentioned crystals, blue and white colors are brighter. They are named “structural colors”. Structural colors can be mixed. For example, by laying structural blue over a yellow pigment, the result obtained will be a vibrant green.
When it comes to the shifting of pigments, small bits of dark-colored melanin can be scattered through the tendrils of big cells containing melanophore. Melanophore is a tissue cell containing black or brow melanin which is involved in color changes in the case of many reptiles and fishes. Or, on the contrary, the packets of melanin can pile up in the center and make the skin lighter. This is not present only in the case of chameleons. Other reptiles and even fishes change their skin in darker or lighter tones when they are stressed or in order to match the surroundings.
The male panther chameleon can change from one color to an entirely different color, such as turn from green to strident yellow. This happens mostly in cases when the male wants to attract a potential female or to intimidate a rival. So far scientists have believed that this is also owing to dispersion, only this time with red or yellow pigments. But the new study shows that this is not the case.
First of all, the study has showed that there were no big cells that contained red or yellow pigment that could explain the shade change.
Using an electron microscope, the researchers analyzed iridophore or pigment cells and discovered how important the crystals are. Regardless of the angle from which you look at them, the crystals form a straight and regular pattern, just like the alignment that formed structural colors. So the researchers further tried to determine whether the crystals were responsible not only for the changes in the bright colors, but for the changes in all the other color as well.
Examining the color changes, they could not explain how green turned from blue into yellow and finally into orange only using the available pigments in the skin. But they found a match by taking a closer look at how crystals shifted. Most importantly they found a change in the crystal pattern when they compared the skin of a chameleon at ease and the skin of a chameleon when facing an enemy. Prof Milinkovitch explained that this works as a selective mirror. Depending on the distance between the layers the mirror will reflect either small wavelengths such as blue or larger wavelengths such as red.
The investigators have also shown how the color of the skin can change because of geometrical shift. When placing the cells in salty water that sucked the liquid out of them, the crystal packing was modified and the color change was produced just like in the case of the reptiles.
The second layer of cells, containing bigger and disorganized cells, reflects the sun rays and keeps the chameleon cool. The two layers of cells is something particular only to chameleons. Other reptiles have either regularly organized crystals to create bright colors or disorganized crystals that reflected the sun light. In the case of chameleons we fin both extremes. According to Prof Milinkovitch this is something that has never been met before in evolution. Chameleons can choose if they want to stay unnoticed or if they want to catch the attention through strident colors and at the same time they can control the temperature of their body.
This discovery is important because it could help physicists and engineers copy the color changing capacity of the chameleon and use it in technology. It could be used for example to develop appliances that expel reflection.
Image Source: Chameleon Forums